3GPP introduced the LTE (Long Term Evolution) that provides core network entities for supporting real-time voice and multimedia IP services.
Currently, RRC connection re-establishment procedure as described by 3GPP TS 36.331; in the following reference is made to TS 36.331 release 10. Aforementioned reference shows some bottlenecks being implemented, because it might bring some conflicts with respect to management of UE timers (specifically the so-called T311 timer for supervising a RRC connection re-establishment as specified in TS 36.331, and a barred timer supervising that a barred cell is not selected within a certain time) used to handling a barring of a cell when essential system information are missing.
On the other hand, this procedure takes some time due to cell selection process, which needs system information (comprising a so-called Master Information Block—MIB—and a number of System Information Blocks—SIB—). The UE needs to locate and read relevant system information before re-establishing any connection to the access network (E-UTRA).
The purpose of RRC connection re-establishment procedure is to re-establish the RRC connection, which involves e.g. a resumption of SRB1 operation, a re-activation of security and a configuration already given by network.
It is desired to reduce the duration of this process in order to improve overall quality of service offered to the end user.
Specifically, according to above-cited TS 36.331, the UE shall only initiate the procedure when AS security has been activated. The UE initiates the procedure when one of the following conditions is met:                upon detecting radio link failure, in accordance with section 5.3.11; or        upon handover failure, in accordance with section 5.3.5.6; or        upon mobility from E-UTRA failure, in accordance with section 5.4.3.5; or        upon integrity check failure indication from lower layers; or        upon an RRC connection reconfiguration failure, in accordance with section 5.3.5.5.        
TS 36.331 specifies a timer referred to as T310 and further specifies above mentioned timer T311. The timer 310 is started if physical layer problems occur (receiving consecutive out-of-synch-indications); the UE will go to RRC idle mode after expiration of this timer if access stratum (AS) security has not been activated, otherwise start T311 if AS security has been activated. AS security may comprise the establishment of an integrity protection of RRC signaling (messages) and ciphering of a RRC signaling and user data, so that the UE and the network may exchange data.
T310 values are selected by the network and may be chosen as one of 0 ms (milliseconds), 50 ms, 100 ms, 200 ms, 500 ms, 1000 ms, 2000 ms according to TS 36.331. Upon expiration of T310, T311 is started to supervise that RRC re-establishment procedures are performed in time. According to TS 36.331 the network may choose T311 value as one of: 1000 ms, 3000 ms, 5000 ms, 10000 ms, 15000 ms, 20000 ms, 30000 ms Both T310 and T311 values may be provided for the network to the UE.
Specifically, upon initiation of the procedure, the UE mainly shall:                stop timer T310, if running;        start timer T311;        further:        suspend all RBs except SRB0;        reset MAC;        apply the default physical channel configuration as specified in section 9.2.4;        apply the default semi-persistent scheduling configuration as specified in section 9.2.3;        apply the default MAC main configuration as specified in section 9.2.2;        release reportProximityConfig and clear any associated proximity status reporting timer;        
In addition, the UE shall:                perform cell selection in accordance with the cell selection process as specified in TS 36.304, current version 11.        
Starting timers in the UE might be regarded as to count down from predefined values and either to supervise that certain actions are performed before expiration of a timer (reaching “0” value) and/or performing certain actions after expiration. Starting T311 might mean to count down from a predefined T311 value and to supervise that a selection of a suitable cell or a cell using another RAT is performed before expiration. Timer T311 might be stopped e.g. after such suitable selection. If the selection cannot be performed before the expiration of the timer, the UE shall enter the RRC idle state (RRC_IDLE).
The cell selection process as specified in TS 36.304 includes fresh system information (MIB/SIB) reading. In section 5.2.2.2 of TS 36.331, it is stated that the UE shall apply the system information acquisition procedure upon selecting and upon re-selecting a cell, after handover completion, after entering E-UTRA from another RAT, and upon return from out of coverage.
Hence, when the timer T311 is running, the UE shall re-read system information.
In section 5.2.2.2 of TS 36.331 it is further specified that a cell shall be barred, if essential system information is missing (as indicated in TS 25.331 current version 11, this may similarly apply to 3G systems). Such barring might be controlled by a so-called barred timer in the UE that may be started upon a detection of problems to get the essential system information. The value of this barred timer is not specified in the standard and may be UE implementation specific.
A problem is that the UE cannot select the previous serving cell in case of barred timer value being greater than the T311 timer value given by network; in such case the UE goes to IDLE state (after T311 expiration) and looses the RRC connection, despite of a relation to the previous serving cell (this cell may be a good cell to be selected to resume the RRC connection).